As a dielectric resonator oscillator (DRO) used in a radar system or a communication system using a microwave or a millimeter wave, a device disclosed in U.S. 2003/0048217 A1 (Japanese Patent Application Laid-Open Publication No. 2003-84058) is known for example. FIG. 11 shows a first example of the DRO disclosed in the document. A dielectric substrate 25 is disposed adjacently to an MMIC (Microwave Monolithic IC) chip 2, and a transmission line 8 and a terminating resistor and earthing means 9 are formed on the dielectric substrate 25. The MMIC chip 2 is electrically connected to the dielectric substrate 25 with wires 14. By disposing a columnar dielectric resonator 1 close to the transmission line 8 on the dielectric substrate 25, the transmission line 8 is electromagnetically coupled to the dielectric resonator 1 and they are operated as a resonator. Further, a varactor diode 5 to regulate an oscillating frequency by voltage applied from a terminal 11 is connected to a line in the MMIC chip 2 connected to the transmission line 8. A similar configuration is disclosed also in U.S. Pat. No. 5,291,153 (Japanese Patent Application Laid-Open Publication No. H04-326607).
FIG. 12 shows a second example of the DRO disclosed in U.S. 2003/0048217 A1. A transmission line 8 and a terminating resistor and earthing means 9 constituting a resonator are formed on an MMIC chip 2. A dielectric resonator 1 is disposed on the MMIC chip 2 close to the transmission line 8 or on a dielectric substrate 25 disposed outside, and the transmission line 8 is electromagnetically coupled to the dielectric resonator 1 to form a resonator.
Meanwhile, Japanese Patent Application Laid-Open Publication No. H11-205039 discloses a microwave oscillator having a transmitting circuit formed by connecting a dielectric resonator to an end of a microstrip line and coupling the other end thereof to an active element through a capacitor, wherein a stub is formed at an end of the microstrip line, the length of the stub is set at an appropriate length, and an oscillating frequency is regulated.
Further, Japanese Patent Application Laid-Open Publication No. H08-293728 discloses an MMIC voltage controlled oscillator wherein a tuning circuit is incorporated into the interior of an MMIC, and a microstrip resonant line constituting a resonator or only a dielectric resonator is formed on the external circuit of the MMIC.